This invention relates to the distribution, or feeding, of electromagnetic power from a source of the power to an array of power utilization devices, such as radiators of an array antenna and, more particularly, to the feeding of power by a planar system of rows and columns of microwave couplers at a fixed frequency or frequency band allowing for a steering of a beam of radiation from the array antenna in one plane, perpendicular to a plane of the radiators of the antenna, while allowing for differential phase shift and amplitude to signals applied to adjacent radiators by the feed assembly.
A two-dimensional array antenna may be described in terms of an XYZ coordinate axes system having an X axis, a Y axis and a Z axis which are orthogonal to each other, wherein the radiators are arranged in rows along the Y direction and in columns along the X direction. It is common practice to construct the antenna with control circuitry for controlling the amplitude and the phase of the signal radiated by each radiator, the control circuitry including, by way of example, an electronically controlled phase shifter and an electronically controlled attenuator or amplifier. The control circuitry extends in the the Z direction, perpendicular to the plane of the radiators and the radiating aperture of the antenna. To insure a well-formed beam without excessive grating lobes, the spacing of the radiators and the corresponding spacing of the control circuits is less than approximately one free-space wavelength of the electromagnetic radiation radiated by the radiators, for example, less than or equal to 0.9 wavelengths for a beam of radiation which remains stationary relative to the antenna. However, for an antenna which is to provide a scanning of a beam relative to the antenna, the spacing normally is less than one wavelength but greater than or equal to one-half wavelength along a coordinate axis for which the beam is to be scanned.
A problem arises in that the foregoing control circuitry may have excessive weight and physical size for some antenna applications, particularly for antennas which provide a scanning capacity along one or two coordinate axes. For array antennas providing only a stationary beam or a beam which is to be steered in only one of the coordinate directions, X or Y, a planar configuration of a radiator feed system is preferred to reduce both size and weight of the antenna. Planar feed systems have been built, such as a set of parallel waveguides disposed side by side, and having a set of radiating slots disposed along walls of the waveguides to serve as radiators of the antenna. Steering of a beam can be accomplished by varying the frequency of the radiation, this resulting in a sweeping of the beam in a direction parallel to the waveguides. Such a feed system presents a specific relationship between frequency and beam direction, and cannot be used in the general situation in which beam direction must be independent of frequency. A further disadvantage of such a feed system is the lack of a capacity to adjust individually the values of phase shift and amplitude of signals between adjacent ones of the radiators. Such a capability of adjustment of phase and amplitude is important for developing a desired beam profile. Stripline or microstrip feed structures have also been found useful in the construction of planar feed systems because the physical size of a power divider in stripline or microstrip is smaller than the aforementioned one-half free-space wavelength. However, existing stripline and microstrip feed structures do not permit the desired beam formation, scanning, and radiator layout in combination with the capacity for adjustment of phase and amplitude to signals of adjacent radiators.